Bird Flight By now you've had weeks to witness the flying skills of Tree Swallows. You've seen them soar, dive, and dash about. You've watched them bank, wheel, turn, pivot, and hover. You can't help but be impressed by their dazzling powers of flight. Since they truly are masters of the air, how can a web site about Tree Swallows not attempt a page about flight? Photo below by Homer Caliwag. Make it a point when you visit your project to devote some time to simply watching swallows fly. Observe how they hold and move their wings as they execute different maneuvers. And watch how other bird species fly. Compare their skills and techniques with the swallows'. How do you think body size, wing size, and wing shape influence each bird's flying style? To say flight is complex is a gross understatement. Flight involves a great many intricate interactions among a bird's nerves, muscles, tendons, skeleton, and feathers. Almost every aspect of bird anatomy and physiology has been extremely modified over time as their flying ability increased.

But though people have admired bird flight for thousands of years, it wasn't until the 1980's, when scientists were first able to make slow motion x-ray movies of birds flying in wind tunnels, that they truly began to understand just how all a bird's parts worked together in flight. We caution you that the content that follows barely scratches the surface of bird flight. In our opinion by far the best and most complete treatment we know regarding this fascinating subject is found When you really consider it, flying seems an impossibly difficult thing to do. To fly successfully an animal must be able to resist the force of gravity and support itself in air, a movable, flexible, and not very supportive medium. And once airborne an animal must be able to both power and control its movement. Many animals can glide, but of all the animals that have ever lived on earth only insects, pterosaurs, birds, and bats have developed the ability to truly fly, evidence of flight's difficulty. And to achieve something this hard the bodies and metabolisms of these groups had to undergo drastic modifications. The most obvious adaptations for powered flight are wings.

Powered flight requires wings of some kind, flat surfaces that can be pushed against air, providing upward lift, forward thrust, and continuous control of movement. The smaller "contour feathers" on the bird's head, body, and wings smooth and streamline its shape, so it can pass through air with less frictional drag. Some groups of these contour feathers, the "coverts," partially overlap the wing and tail flight feathers, adding to the bird's streamlining. Try distinguishing these feather types in pictures on this web sites. Birds have other vital adaptations for flight that aren't obvious to us because they are internal. Bird bodies are extremely modified for lightness and strength. Over time many bird bones became smaller in size or were lost altogether. Most remaining bones are thin-walled, hollow, and reinforced with tiny cross- struts. But it's in their breathing and heat-regulating systems that birds are most surprisingly and radically different from us. Bird flight muscles demand huge amounts of oxygen to fuel powered flight. This muscular exertion generates tremendous amounts of internal waste heat that must be removed from their bodies. Birds meet these related needs using a combination of lungs and air sacs, a system possessed by no other group of living animals.

When we mammals inhale air enters our lungs and oxygen and carbon dioxide are exchanged in tiny dead-end sacs. Then the used air is exhaled back out the exact same route. Our lungs never empty completely so stale air being exhaled mixes with the next fresh breath, and we extract only a low percent of the oxygen available per breath. Birds have much more complex and efficient respiratory systems, in which a bird's muscles and skeleton pump air through in a continuous one-way direction, not back and forth like ours. Birds' one-way flow allows them to extract almost all the available oxygen from air inhaled. Bird lungs do not have tiny dead-end sacs like ours for gas exchange. Instead, air flows through tubes in bird lungs called "parabronchi," where oxygen and carbon dioxide are exchanged across the walls of microscopic capillaries. And during a bird's breathing cycle air passes not just through its lungs but also through a complex system of interconnected "air sacs." Most birds have nine pairs of these thin-walled sacs. The sacs fill parts of their body cavities, and even penetrate their muscles and bones. A substantial part of a bird's body is actually filled with air.

As a bird flies its flight muscles and moving skeletal parts act like a bellows, rhythmically pumping air along through its lungs and air sacs. Although oxygen and carbon dioxide aren't exchanged in the air sacs, the routing of air through them is what permits a bird's one-way, rapid-ventilation, breathing system. Air sacs have still another vital function: dissipation of heat. Air flowing through the sacs picks up most of the heat a bird's muscles generate during flight and is conducted outside when the bird exhales. Clearly bird bodies have been drastically modified for flight, but what about flight itself? How do birds do it? Flight actually has three parts: takeoff from the ground or a perch, sustained powered flight, and landing, and each requires somewhat different actions by the bird. The airfoil shape of bird wings helps. Wings are more curved on top than on the bottom, which means air passing around has to go a bit farther and faster over the top. This creates a pressure differential, with higher pressure below and lower pressure above the wing, that helps lift the bird's body up.

But, although airfoils alone are used to great advantage by gliding and soaring birds, they aren't enough for continuous powered flight, . True powered flight also requires a direct input of muscular force to get a bird into the air, keep it there, and propel it in a controlled manner toward where it wants to go. Taking off from a standstill requires an immense generation of force, and since the bird isn't moving forward through the air yet, it must use its own muscle power to lift itself up. A bird taking off typically makes a very exaggerated up-sweep, raising both wings high over its back (below left). The wings are then driven downward with a long powerful stroke (below right) which lifts the bird into the air. Birds on elevated perches can takeoff more easily, by simply dropping off the perch, spreading their wings to create lift (below), and letting gravity provide the initial forward momentum. Once airborne birds must flap their wings if they want to keep flying under their own power. This may seem simple enough, but flapping is actually a complex, multi-part action. What's the tail's main role in flight? Bird tails don't flap.

In flight they coordinate with the wings or operate semi- independently, depending on circumstances. During steady, straightforward flight the tail doesn't have much to do. But when turning is required or air turbulence causes flight instability, movements of the stiff tail feathers, technically called "rectrices," help the bird steer like a rudder and maintain directional control. Landing: Eventually of course flying birds must land, and to land successfully they must slow down dramatically while maintaining enough control to avoid crashing. Many birds accomplish this by making deep wing beats and fanning their tails to decelerate, then throwing their legs forward to absorb impact and contact the landing surface. Photo below by Don Christian of SouthernShots21. Some situations allow birds to swoop up as they land (see below), which lets gravity help slow their forward momentum. Questions for the next Topic: Mating . DNA studies of Tree Swallows show the nest female is almost always the mother of all the young in her nest, but the nest male often is not the father of all young in his nest. What's going on here?

Biology of Animals & Plants - Vertebrates Vertebrates - Chordates with a Few "Extras" Vertebrate s, being a subphylum of the Chordates , have the basic list of chordate features , but have a few others as well: - Vertebrate ectoderm forms a skin with two layers , an epidermis over a dermis. - A vertebral column / backbone, which is both the central component of the skeletal system and a protector of the spinal cord, the trunk of nerves that runs under it. - A skull, usually, to protect the brain. - Usually limbs or fins in matched pairs, which usually show serial homology . - A circulation system with heart chambers, red blood cells to carry oxygen, and white blood cells to aid immunity. - An endocrine system of hormone-producing glands. There are Many Vertebrate Subgroups Here is a list of the basic vertebrate subgroups with some distinguishing features: - The jawless fish , not quite full-fledged vertebrates but much closer than lancelets are.

These lack jaws (their teeth are embedded in tough rings around the mouth opening) or paired fins, and have other features not found in advanced vertebrates (for example, they retain their notochords through their lives). - The cartilage fish , whose skeleton is made of cartilage, making it less rigid than the bone skeletons of other vertebrates. Although thought to be more primitive than other groups, some of the cartilage fish have been shown by recent research to be much more "evolved" than folks really expected. There are comparatively few fresh water species - this is considered a marine group. - The bony fish , with bone skeletons. This group appears to have evolved in continental fresh water systems and then moved back out into the oceans. They developed the water-proofing and shallow-water adaptations that made land vertebrates possible. At a critical point in evolutionary history, this group could have either become slow-moving but heavily-armored, or quick but more vulnerable - the former seemed to be the most "popular" construction. However, the survivors were mostly in the last group, but who knows why? Of the vertebrates, the bony fish have the most named species. - The amphibians , the first vertebrates to really exploit land environments.

However, like early plants, they remained limited by a need to find open water for the spread of sperm to egg cells. Eggs are fertilized in water and usually an aquatic larval form develops, which may or may not go through metamorphosis to become a land-living adult. Many amphibians require wet environments (and breathe through their thin, moist skin), but many have adapted to dry conditions where open water is available only when mating is done. One odd characteristic of the group is that adults usually have relatively huge mouths. - The reptiles are one of the vertebrate groups fully adapted to land - their epidermis produces a nice waterproofing layer of scales, breathe with internal lungs, transfer sperm into the females body with no need for open water (this is called internal fertilization), and produce amniote eggs that have special membranes to minimize water loss. Reptile breathing, with a rib cage around the lungs, is more efficient than most amphibian respiration. Reptiles have been a very successful land group - especially if one includes the dinosaurs as reptiles - and has been limited only by cold climates.

- The bird s, which are quite likely a surviving subgroup of the dinosaurs (who themselves were probably not still reptiles), who produce a highly specialized scale type, feathers, and have many other adaptations that allow them to fly. It is unclear how many features used in flight might have developed in dinosaurs as a way of making very large animals light enough to move quickly - did birds evolve traits for flight, or just modify traits that were already there? In any case, birds are also internal fertilizers and produce amniote eggs. They also are endotherms (commonly called warm-blooded, but that term can be misleading), which means that their bodies work at a set internal temperature that energy is consumed to keep stable. Endotherms get some advantages, the biggest being a permanently-high metabolism, very good if you might need to take to the air at any moment (the feathers also serve as insulation to minimize heat loss, and may have evolved in ancestral dinosaurs for this reason). The downside is that a lot of food (and oxygen) is needed to generate that energy, much more than similar-sized ectotherms ("cold-blooded," who mostly work at temperatures matching the environment around them).

Birds have a heart with two separate sides to keep their lung circulation separate from their body circulation and maximize the oxygen-carrying function of the blood. Birds move on the ground on their back legs, as their dinosaur ancestors did, and their front legs have evolved into wings. The need to produce wing power has fused most of the bones of the body - birds are flexible in their neck, wings, and legs but cant twist their bodies like other vertebrates - and the front of their rib cages are modified to anchor very large wing-pulling muscles. Birds are also full of air spaces , not just in their bones (you probably knew that birds "have hollow bones," but so do you - only theirs have air sacs in them to make them super-light) but in many body cavities - air is much lighter than the fluids which would otherwise be there. Some of these air spaces are connected to the lung system, further increasing oxygen capacity. The lack of teeth, which are denser and heavier than any other vertebrate part, is probably also also for weight purposes - beaks are made of a much lighter cartilage-type material.

- The mammal s are also endotherms, also with insulation, in the form of fur or hair, and a similar circulation pattern. Mammal skin is often embedded with glands, and a particular type has become a marking feature of the group: mammary glands produce nourishment for the young mammals. The vast majority of the group also do not produce eggs, but rather produce live young that develop either in a pouch or inside a specialized internal organ, the uterus, a structure which is used for egg processing in other animals. A less well-known feature is that mammals, unlike other animals, can have a variety of different types of teeth in each mouth (and usually get just two full sets during their lives), making them perhaps more evolutionarily flexible. Jawless Fish - Some Primitives Hang On There are only two small groups of jawless fish still around, but long ago there were many more. In the distant past, these fish commonly had armor coverings, but all of those fish went extinct. The surviving jawless fish (also called Agnathans) are - - The hagfish or slime eels. These marine fish are primarily scavengers. They can protect themselves by producing amazing amounts of nasty mucus when threatened.

They can be a nuisance when trapped in nets or lobster traps, but are a popular food fish in Korea. - The lamprey eels . These are found in both salt and fresh water, and are one of a very few types of vertebrates that are attachment parasites. They attach to larger fish with a mouth that is like a many-toothed suction cup and rasp away at the hosts tissues, sucking in blood and whatever else comes loose. Cartilage Fish - Not as Primitive as Their Reputation People swimming often cant help but worry about whats hidden beneath them, and in the ocean that fear often takes on the image of a shark. And they are out there, but remember that your chances of being lunch are much tinier than your chance of being crunched in your car on the way home. Sharks belong to the cartilage fish subgroup. This group, and sharks in particular, have been around a very long time , probably an example of a successful form in a fairly constant environment requiring little obvious change. However, just because sharks of today look like their ancestors doesnt mean that they havent been evolving. Recent research has found that sharks can be quite bright, that they may have complex social structures, and that some have endothermic brains.

They do have cartilage skeletons , which are perhaps less efficient than bony skeletons, but they lack the buoyancy that allows bony fish to have harder and heavier skeletons. When a cartilage fish stops swimming, it sinks (which is not so bad if its close to the bottom...). There are many types of sharks, from the freely-swimming predators that everyone thinks of to many bottom-dwelling species. They range from fairly small species up to the worlds largest fish, the whale shark , a huge animal that filter feeds on tiny plankton. A swimming shark keeps itself "aloft" while swimming with fins that act in many ways like an airplanes wings. The other subgroup of cartilage fish is the rays and skates , which swim with a flying motion similar to a birds. For the most part, though, these are bottom-dwellers, laying camouflaged on the ocean floor. Although there are differences between rays and skates, they look pretty much the same. Bony Fish - A Success Story It is thought that the bony fish evolved in fresh water.

Adapting to a very dilute environment may have led to some dilution of tissue and cell fluid (of course, it couldnt function if it was as dilute as fresh water), and even the modern marine species still have tissue fluid more dilute that the water around them (most marine invertebrates are in a dilution balance with their surroundings). Bony fish are the largest vertebrate group, with by far more named species than any of these other groups. They have a couple of important features that have helped them to prosper. Obviously, bony fish have a calcified bone skeleton, which provides better muscle leverage than cartilage. It is heavier, but the next feature offsets the extra weight. Bony fish usually have a gas-filled internal organ called a swim bladder . This is used to adjust the buoyancy of the fish to the water around it (deeper water is denser, affecting buoyancy) so that, unlike cartilage fish, a bony fish doesnt sink when it stops swimming, it can just "hang," reducing the amount of energy it has to expend. Oddly enough, the swim bladder is thought to have arisen as a lung, used by fish whose water bodies dried out periodically.

This seems unlikely, but the progression of evolution of this group is pretty confusing. Whereas cartilage fish have gill slits, bony fish usually have an operculum (opercle), a rounded cover over the gills. This may make water flow across the gills more efficient, and it often seems to make pumping water through the gills (essential if a fish isnt swimming) work better. The two major subgroups of bony fish include the lobe-finned fish , whose fins are supported by limb-like structures that protrude from the body. Few species in this group still exist, although at one type it was quite a successful group. The other group is the ray-finned fish , whose fins have no such limb-like structures. At one time, the lungfish were considered a third subgroup, but rarely are any more - strangely enough, some books now include them with the lobe-finned, some with the ray-finned fish. The progression from fish to 4-legged land vertebrates (tetrapods) is a subject of much controversy. Lungfish were once the leading candidate as ancestor types, but there seem to be too many anatomical differences between them and early tetrapods.

Lobe-finned fish are thought to be the ancestral type by some, with the lungs evolved from the swim bladder (which some think evolved from a lung - told you it was confusing!), ray-finned by others, with lungs evolving from brood pouches, "cheeks" where eggs and babies could be protected and supplied with oxygen from the linings. Probably the first vertebrates to really live in the world beyond the lakes and seas were the amphibians. For a while, when they had the run of the place, some got to be as big as cars, but many species were eventually replaced by later animals with better abilities for a terrestrial (land-living) existence. Amphibians, like early plant groups , were able to handle some aspects of life on land, but some problems kept them mostly in moist areas with at least periodic open water available. The amphibians have two major subgroups: the frogs and toads and the salamanders and newts . Frogs and toads are hoppers, with large back legs and short front legs. In general, frogs favor wetter environments and are less resistant to drying than toads.

Toads tend to use their skin less as a respiratory surface, allowing the skin to be more waterproofed. These amphibians usually go through a fish-like larval stage, commonly called a tadpole . Salamanders and newts are lizard-shaped crawlers, and sometimes confused with lizards, although they are not scaly. Salamanders usually live on land as adults, while newts often spend just some time on land before living in water as adults - they usually have flatter tails, used for swimming, than salamanders. Amphibians skin is very glandular - the glands help keep the skin moist. But these glands have often been adapted for defensive purposes, and many amphibians are noxious if not actually poisonous if eaten. Some South American frogs produce poisons so nasty that a person can get ill from just handling them. And like many nasty creatures, including many in other groups , they are colored to stand out in their environments (called warning colors / displays); predators tend to avoid "prey" that can be easily seen - or they soon learn to. Warning colors tend to be very contrasty and bright, and can be found in things like millipedes, centipedes, bees, and skunks.

A current scientific mystery is why, in recent decades, worldwide amphibian populations seem to be shrinking . All sorts of explanations have been given: global warming, greater sun ultraviolet radiation due to loss of atmospheric ozone, pollution, parasites / disease, and others. Reptile s - Multiple Groups Under the Same Heading? With lots of four-legged critters running about on land those many years ago , did the amphibians give rise to the reptiles and the reptiles to the dinosaurs, the birds, the mammals? That seems to be the accepted story . The transition from amphibians to reptiles has not been found in the fossil record, but may have involved small salamander-type amphibians that were unlikely to fossilize. The amniote eggs , waterproof but able to breathe, that made real land-living possible are a feature found in all of these groups. Reptile eggs (and mammal eggs in the couple of species that make them) are leathery. The internal structure used by live-bearing vertebrates, including the mammals, is still based on amniote membranes and connections.

The subgroups of reptiles are a motley crew that share the same type of scaly skin and some skeletal features, but are different enough that they could easily all be considered separate classes. And the more that is discovered about dinosaurs, the more it seems that they, too, were a distinctly separate group. Probably the reptile prototype is the lizards and snakes . Lizards are long, slung between the "elbows" of their legs, and during the ages of dinosaurs included forms that flew through the air, the pterosaurs , and swam in the seas, the mosasaurs and plesiosaurs . The snakes are obviously related to the lizards, but how the transitions happened is not clear - one of the more recently-proposed theories makes some subgroup of mosasaurs the ancestors of snakes. The crocodilians , which include the alligators as well as crocodiles and several other similar animals, moved back from the land into the water, where they have become formidable predators. This is an extremely old group of reptiles. The turtles are the least like the other reptiles, with several unique features besides their shells, which are actually highly modified scales supported by a modified rib cage.

In general, the water-living turtles are predators, and the land-living tortoises are plant-eaters. The Ups and Downs of Bird s The idea that the birds were descended from dinosaurs is both fairly new and very old. One of the oldest true bird fossils, Archaeopteryx , had been classified as a dinosaur until a low-angle lighting of the fossil showed the imprints of feathers around it. Recently, it has become more and more accepted that the two-legged dinosaurs, of the group that includes Tyrannosaurus rex, often, maybe always, had feathers, and they had an offshoot group that took to the air (the "flying dinosaurs," pterosaurs, as mentioned earlier, were really lizards). Some fossils found recently in China seem to indicate that feathers were fairly common in 2-legged dinosaurs and may have started as insulation or camouflage and been put to work on wings later. By the end of the Age of Dinosaurs, several groups of birds had evolved. Their size and flying ability seems to have gotten most of them past the mass extinction that wiped out the others, making them the only surviving dinosaurs.

Ironically, much later, in some isolated parts of the world such as New Zealand and South America (before it connected to North America), huge flightless birds that "in person" would have been very similar to tyrannosaurs were the top predators, living a very tyrannosaur-type existence. A feature of many modern birds is migration . This movement from one place to another may be done for breeding purposes, but usually its just to follow the food. The birds that stay behind during the temperate winters can still find food, while the migrants depend on something that isnt around (bugs) or accessible (worms or algae or fish) during the cold season. Migrant birds find their ways using many navigation methods and types of programming. For some, the direction and duration of flight is almost all instinctive, while for others its learned from elders (which makes it an epigenetic trait). Some navigate using landmarks, some use the night sky, some have internal compasses. Birds can be quite intelligent and have complex social groups. Some parrots can not only mimic human speech but seem to recognize how the language works on a simple level. Crow babies stay in a family unit for years, learning how things are done.

In captivity, they have been shown to have a complex understanding of tool use. They do a lot with very small brains, which makes one wonder if the assumptions about dinosaurs being pretty stupid isnt a bit stupid itself. Our Fuzzy Group - The Mammal s At one time, the reptiles that would go on to be "reptiles" but the ones that would go on to be mammals were very similar, so much so that fossils had to be divided up based on a kind of artificial benchmark. The bones that are in a modern mammals middle ear are on the jaw of a modern reptile, so it was decided that fossil classification would use that detail to decide what was what. Sometimes that produces some very lizardy-looking mammals (the famous fin-backed Dimetrodon that seems to be in every kiddie bag of plastic dinosaurs is an example) and some doggy-looking reptiles. It took a bit of evolution for the groups to pick up their distinctive features. Through the Age of Dinosaurs, mammals succeeded by staying out of the Big Boys way - our ancestors from that time period were small, probably night-hunting bug eaters and scavengers.

When the dinosaurs became extinct, our ancestors had the perfect jobs to survive those bad times, eating the dead or eating the insects that ate the dead. Afterward, mammals evolved into many of the niches that the dinosaurs had previously occupied, although they never quite got as big (on land, that is). The early mammals were almost certainly egg-layers, and there still exist a couple of mammals that lay eggs: the famous platypus and the less-famous echidna . In these primitive mammals, newly-hatched babes lap up a milky secretion produced by the mother; more modern mammals collect the milk ducts at the surface in nipples. The egg-laying mammals , called monotremes , were eventually succeeded by mammals whose young stayed in the mothers reproductive system for a while, then crawled out and up into a pouch, where they latched on to a nipple and continued to develop. These were the marsupials , which once were "state of the art" mammals. Later, placental mammals evolved, who could keep their young in the females system and feed them with connections to the mothers blood though a placenta. On the wandering continents of Australia and South America, marsupials were pretty successful.

In the rest of the world, placentals arose and replaced almost all of the marsupials. When South America collided with North America and a land bridge, Panama, allowed mixing of the animals, the placentals moving south seem to have driven the remaining marsupials (except for the opossum) out of business. Australia is still fairly isolated, dealing mostly with late-arriving placentals that flew in (bats) and those that humans have brought in, but that causes problems as rabbits and rats and dogs compete with native mammals. There are several orders of placental mammals. Some are small, with one or just a few species, such as the elephants or aardvarks. The larger orders include such odd mammals as the bats (no, theyre not birds, theyre furry) and the whales, as well as flippered orders such as the seals. The biggest orders are the bats (that flying ability is still quite an advantage - they just needed to find the right work shift that the birds had not used much) and the rodents, which include mice, rats, porcupines, and beavers. There are a few different orders of mammals with hooves, divided by how many functional hooves each foot has.

And there is our group, the primates, characterized by our opposable thumbs (and opposable big toes, usually), good eyesight, and relative intelligence. Flight, that is the Question | Dragon Theories | The Circle of the Dragon Circle of the Dragon > Dragon Theories > Flight, that is the Question Dragon Theories Flight, that is the Question Flight is a novel evolutionary development, with only three known vertebrate instances in the billions of years on this planet. Since flight is a factor in many dragon stories, it is important to take a look at possible methods of flying. Footnotes Flying vs. Gliding Before analyzing different methods of flight, it is important to consider what different cultures and traditions may consider 'flight' or 'flying' in relation to modern conceptions. For many centuries, the term 'flying' could be applied to any animal that could be airborne and at least appear to safely navigate or land. Thus, many animals are attributed with misnomers, such as the "flying squirrel" and the "common flying lizard," both of which are gliding animals. Similarly, there are several species of "flying serpents," all of which are a part of the Chrysopelea family.

These snakes flatten their bodies by extending their ribs, allowing them to glide through the air. Gliding differs from flying in that a gliding animals navigate through the air but cannot propel into the air from the ground. Fliers, on the other hand, have the ability to propel into the air and traverse upward from a current position. Many gliding species use air foils to keep aloft, such as a simple flat of skin that can be stretched out, as in the case of Draco Volans. [11] While some animals can glide but cannot fly, animals that can fly do glide. [12] So while many species are now known to be gliders, such as "flying squirrels" and "flying fish," the ability to fly has previously been attributed to them. It is likely that many dragon stories could be referring to a gliding animal. Back to the Top Insects: First in Flight Insects evolved the ability to fly long before any vertebrate species. Over four hundred million years ago, the first insects began to fly.

[2] Unlike the vertebrate species that evolved flight later, flying insects became fully hybridized creatures, with the ability to crawl and move with legs while touched down as well as the ability to fly. [7] Pterosaurs, Avian species, and bats all became ungainly due to the evolution of the forelimbs into wings. While pterosaurs and birds certainly maintained their grounded mobility by becoming bipedal, the same cannot be said for bats, which must sprawl awkwardly on the ground. Insects, on the other hand, retained the ability to crawl easily and fly. Their wings are thin, transparent membranes stretched between rigid veins, making a wing that is strong and flexible. [7] The wings are designed to stir up the air, and the muscles for insect wings are exclusively contained within the thorax, or midriff, of the insect, which means that their wings do not even have muscle tissues to weigh them down. [8] This is why insect can flap their wings far more quickly than other flying creatures, such as birds. The hummingbird has the fastest known flapping speed among birds, flapping its wings about fifty times per second.

[8] Meanwhile, bumblebees flap their wings approximately 150 times per second [1] and some mosquitos can flap up to one thousand times per second. [8] The largest known flying insects were the Meganeura, a genus of dragonfly-like insects that had a wingspan of 75 cm (2.5 ft), which are extinct. [22] While insects evolved flight first, and retained their solid ground mobility, size is an important consideration. The fact that the largest known flying insects possessed a wingspan of roughly 75cm (2.5ft) is a strong indication that draconic creatures did not descend from this lineage. However, the functional adaptations of flying insects, such as the concentration of the flight muscles in the thorax to reduce the wing's mass, make insects worth mentioning. All other species known to fly have evolved an extreme set of adaptations for the sake of being more aerodynamic. Back to the Top Pterosaur Flight From the time when fossils of pterosaurs were first discovered in 1784 [18] , scientists had assumed that pterosaurs had a bat-like wing structure.

This became perplexing, as investigations into the aerodynamics of the species revealed that a bat-like wing structure would make them particularly poor fliers. Kevin Padian is attributed with unraveling the mystery of the mistaken pterosaur flight design, while pushing his streamlined variation of the pterosaur, [17] revealing it to be a truly separate evolution of flight from bats and birds. Like bats, pterosaurs had a skin wing that stretched out from "fingers" (aka digits and phalanges) and the forelimb to the hindlimb or torso/hip. [16] Unlike bats, however, pterosaurs did not evolve a skin attachment that required exact positioning of the hind limbs for flight (bats must be splayed). Much like birds, pterosaurs had a dual locomotion set, with bipedal walking and forelimb-driving flying.

[20] The largest known pterosaur, and the largest known flying animal to have ever existed, is Quetzalcoatlus northropi, with a wingspan of almost 12 m (39 ft.) and at a weight of approximately 127 kg (280 lbs.) [21] Like the non-avian dinosaurs, the pterosaurs disappear from the fossil record around the time of the K-T extinction, approximately 65 million years ago. Pterosaur flight is an important consideration in dragon flight because, unlike all other known fliers, pterosaurs came in enormous sizes. Of course, many of the species were far smaller than the Quetzalcoatlus northropi, but the ability to grow a wingspan of 12 m (39 ft.) would certain fit into the category of "huge" exhibited by many of the dragons in stories found around the world. Back to the Top Avian Flight Birds evolved flight somewhere around one hundred and sixty million years ago [2] so there is a wide variety of flying avian species, ranging from the hummingbird to the albatross. How do birds fly?

The short answer is "with difficulty." [10] Birds have many extreme adaptations to support their ability to fly, from having air sacs inside the bones that coordinate with the lungs to having fewer bodily organs, depending on the species. Avian species traded off strength and weight for aerodynamic leverage. [10] The largest known wingspan for birds is 3.63 m (11 ft. 11 in), which is the maximum wingspan of the wandering albatross. [3] Most flying birds are much smaller in wingspan, since the larger the bird is, the harder it is to fly. Unlike any other creatures, birds uniquely evolved and adapted feathers. No known living creature outside of the avian family has feathers, and even non-flying birds have feathers. Currently, there is much evidence to suggest that feathers evolved from reptilian scales, and feathers and scales are certainly related. [15] Therefore, there is a strong likelihood of the existence of many species of reptiles-with-budding-feathers and early avian species with reptilian scales. Back to the Top Mammalian Flight Bats are the only known mammals that have evolved powered flight. Bats evolved flight fifty-five million years ago.

[2] Like pterosaurs, bats have wings comprised of stretched membranes. The fifth finger (the 'thumb') of a bat is not elongated like the others; instead, it is a hook that can be used for climbing. [9] Despite the common expression "blind as a bat," no species of bat is blind, and most species have excellent eyesight. On top of sharp sight, bats also have echolocation, which enables them to fly at night to hunt for tiny insects. [9] The largest known bat species is Giant golden-crowned flying fox (Acerodon jubatus), which has a wingspan of up to 1.5 m (5 ft.) and can weigh around 1.1 kg (2.5 lbs.) [23] Back to the Top Novel Theory: Hydrogen Drifting Although the origins of this theory are not entirely clear, it has been suggested that flight can be achieved in a dragon-like species by way of hydrogen. Hydrogen has been used in flying propulsion systems, most notably the Balloon, also referred to as the hot-air balloon.

Hot air balloons rely on buoyancy - much like a ship floating in the water - to remain in the air, and hydrogen overcame the obstacle of keeping the fire lit constantly to keep the balloon aloft. The trouble with this theory is that it relies on a propulsion system not found in any known species and that does not provide great control over mobility. An animal would have to have the ability to completely control their hydrogen production and retention, including expelling the hydrogen into a suitable bladder to promote buoyancy, and safely expelling the hydrogen out of that same bladder in order to descend. The animal would also have limited, if any, control over movement. Just as a strong current can move a buoyancy-driven boat with dangerous consequences, atmospheric conditions would affect the travel of an animal with hydrogen-powered-flight. Controlled ascent and descend would be the only sure abilities for such animals, so pockets of hot air and the wind would push the flier around considerably. In order to be light enough to fly, the animal would also have to be fairly small, or sacrifice much of is muscle and fat mass at least, otherwise the bladder used to create buoyancy would be enormous. For example, consider a hot air balloon's balloon in relation to the basket contents it is carrying.

Since modern science shows that avian-dinosaurs survived the K-T extinction and evolved into birds, it is safe to assume that from about four hundred million years ago, when insects first flew, some kind of predator inhabited the sky with powered flight. The pterosaurs would have likely been more potent predators, and modern birds remain formidable hunters. The ability to ascend into the sky, therefore, would not be nearly as useful to escape predators as one might think, especially if the creature ascends into the sky with no ability to steer once aloft. In addition, hydrogen is a highly combustible element, and as a gas, the higher the concentration, the higher the change of combustion. Hydrogen gas also forms explosive mixtures with air at certain concentrations. The likelihood of a living organism developing and surviving such a dangerous, yet oddly useless, propulsion system is extremely unlikely, as the organism would have to avoid all sparks, flames, and even sunlight because high concentration of hydrogen and can spontaneously combust with sunlight. On top of that, the creature would have to diligently avoid being spotted by any airborne predators, as it could not steer to escape them.

While a hydrogen-filled bladder is unlikely to enable any living organism to fly, this novel theory does present an interesting concept for non-flying gliders. The ability to gain enough lift to remain aloft without expending a tremendous amount of muscle energy would be highly valuable for a glider or a flier that relies on soaring. However, as no known species has a biological structure that utilizes something like hydrogen to produce thrust (a force that counteracts the downward gravitational force), it is a difficult concept to integrate hypothetically into a flying organism. Back to the Top Dragon Flight: Evolving the Ability to Fly Insects, pterosaurs, birds, and bats, oh my! These known creatures can give us a stronger understanding of the drastic requirements of flight on a living organism. Many animals have sacrificed size in order to fly, and bats have lost grounded mobility for better flight mobility. It is important to remember that while many of these novel developments for flight seem elegant and even intelligent, evolution is not chosen. Pre-avian dinosaurs did not "choose" to adapt scales into feathers, and bats did not "choose" to give up mobility on the ground for the ability to fly.

Changing environments, from the weather to local predator and prey populations, fueled survival rates of certain biological adaptations that resulted in the ability to have powered flight. However, the ability to fly does not mean that the animal can fly well, or that there are not severe restrictions as a result of the development. It is also important to keep in mind that true flying and gliding have been separate on the basis of mechanics. A glider keeps aloft by slowing its momentum towards the ground due to gravity, while a true flier has the ability to power its own flight with muscles and movement. That being said, for many thousands of years animals that could glide well were considered flying animals, so when considering theoretical dragon flight, it is important to consider the possibility of a dragon being a gliding animal. How do animals evolve the ability to fly? Unfortunately, there is not much fossil evidence that revels the exact method of evolution for birds and pterosaurs, although there are several theories out there, the two basic ones being "Ground Up" and "Trees Down." In short, the "Ground Up" theory posits that before an animal becomes a flying animal, it must become bipedal.

Generally, the animal would probably be a quick, bipedal runner, which would allow it to have its forelimbs ready to grab prey as it runs. [14] Incidentally, this same adaptation would allow the forelimbs to be free to develop novel adaptations that would enable the animal to gain lift during high leaps (pre-flight techniques) as well as developing into full-fledged wings. [15] Eventually, the ability to fly by flapping would develop in some species. Meanwhile, the "Trees Down" theory has evolutionary traits that start with plummeting, usually for arboreal species. The next development would be parachuting for safe landing, then gliding, then powered flight. [13] Both theories have generated due controversy, but it has been widely acknowledged that different forms of flight (such as bat flight vs. avian flight) may well have evolved differently. Another key consideration is penguins, which have developed wings that help propel them through the water instead of the air. Clearly, in the case of avian species, bipedalism came first, and the environment influenced the evolutionary adaptations from there. Some birds lived in areas where traversing the air become beneficial, so those birds that developed the ability of powered flight survived.

Other birds lived in areas where the ability to swim promoted survival, so those that developed fin-like swimming wings survived. The progression of biological adaptations for bats is better understood, so it is easier to describe the evolutionary steps from a mammalian gliding ancestor to the powered-flight flapping flier known today as the bat [19] , which fits the "Trees Down" theory of the evolution of flight. However, since flight has evolved independently for insects, pterosaurs, bats, and birds, it is possible that the "Trees Down" theory does not apply to birds or to pterosaurs. Back to the Top Dragon Flight: Thermoregulation Luckily, the abundance of birds today presents a fuller picture of the necessities of flight. Pterosaur fossils cannot reveal if these animals were ectothermic (as modern reptiles, which acquire their bodily temperature through external sources) or endothermic (as modern birds and mammals, which generate and maintain their own bodily temperature). Birds are exclusively endothermic, maintaining their own bodily heat, making it likely that pterosaurs would also be endothermic.

Thermoregulation is necessary because it promotes the use and fluctuation of energy within the animal; an animal that generates its own heat can have more efficient muscle movements, for example. Warmer muscles can provide more energy than muscles are a cooler temperature, which is why birds and mammals are endothermic, maintaining their own internal heat. However, ectothermic animals, which obtain heat from the environment, save energy by absorbing heat from outside sources, meaning that their metabolisms would not demand additional food for body heat maintenance. While there is a substantial amount of controversy over the evolution of endothermic species from ectothermic species, science has revealed the positive aspects of both forms of thermoregulation. Insulation, which happens to be provided by feathers in spades, is necessary for an endothermic creature living in a cool, cold, or seasonal climate. However, ectothermic creatures cannot live in severely cold climates, as there must be some source of heat by which to regulate their own bodily temperature. Birds must deal with not only the energy requirement of flight, but also the incredible amount of heat produced by their muscles during flight.

Many birds have specialized air sacs throughout their bones, enabling a respiratory-related cool-down to prevent hyperthermia. All flying animals would have to deal with both challenges of thermoregulation to survive. Since both bats and birds are endotherms, many have assumed that other flying species would also be endotherms. Due to the heavy energy costs of flight, it is unlikely that an ectothermic animal would be able to fly. However, another possibility for thermoregulation can be found in white sharks. White sharks, and other mackerel sharks, are the only known sharks to have a partially endothermic thermoregulation system. [5] Most sharks are ectothermic entirely, and since they live in the ocean and have no insolation, the body heat generated by their powerful trunk and tail muscles as they swim dissipates quickly into the surrounding water. [5] Unlike true endotherms, white sharks do not maintain a constant body temperature, but because of their modified circulatory systems, select organs have elevated temperatures to improve efficiency. [5,6] The mechanism for this heat exchange is simple. Arteries supplying cold blood to the muscles run parallel to veins draining warm blood from the muscles.

Since the muscles of the shark generate heat, the outgoing blood warms the incoming, cold blood, resulting in retention of heat by way of movement. [6] The main heat exchangers of the shark lie in the trunk muscles, or the large, powerful muscles, of the shark. It is important to mention, however, that white sharks are also subject to constant movement due to their oxygen intake method, dubbed ram ventilation, where a constant move forward pushes water over gills so that oxygen can be absorbed. [4] If the shark stops moving for too long, the heat produced by its movement will dissipate, but it will also soon drown because its gills must have water flowing across them in order to breath. Near-constant motion keeps white sharks alive both by oxygenation and by enabling better heat retention. Drawing on the white shark's modified respiratory and circulatory system, it is possible to consider a flying species that could also be partially endothermic, keeping key muscles and organs at an elevated temperature. This would also reduce the need for a sophisticated cooling system, which avian species possess. However, the animal would have to be in some form of constant motion, or otherwise be producing substantial body heat.

Since weather often affects flying ability, it would be unlikely that such an animal would need to constantly fly. So if there was to be a partially endothermic species, perhaps represented in the mysterious pterosaurs, they would have to have another method of generating high body temperature in case of poor weather or even in times of heavy rain. Back to the Top Dragon Flight: How would dragons fly? Much like birds, it is likely that dragons would fly with difficulty. The wide variety of dragon types makes exploring the possibility of flight even more arduous, since a wyvern and an amphiptere have a wide deviation in body type and size. However, there are some general rules that can be taken away from creatures that are known to fly or to glide. Gliding and flying are separated by the animal's ability to power its own flight. Most gliding animals are small. Most flying animals are also small, especially when it comes to weight. Thermoregulation can add additional strain on an animal, and all known flying animals are endothermic. Powered flight requires severe adaptations. Depending on the type of dragon, its ability to fly would be restricted, above all, by its size.

By and large, both gliding animals and those with true, powered flight tend to be small. The largest wingspan among the known, living bats is 1.5 m (5 ft.) and the largest wingspan among the known, living birds is 3.63 m (11 ft. 11 in.). While neither of these wingspans can be considered "tiny," they certainly do not reflect the idea of an enormous beast that is of unthinkable size. The only known flier to be larger than this is the largest known pterosaur, with a huge wingspan of 12 m (39 ft.). This would certainly qualify it as an enormous monster, especially compared to average sized humans (1.47 m to 1.9 m tall or 4ft. 10in to 6ft 3in tall). There have been large, flying animals on this earth, but the majority of fliers are small. It is therefore likely that dragons would fall into a small range of sizes (approximately 1 m to 3.5 m, or 3.3 ft. to 11 ft. for wing span) and be very light animals.

Question: Which is the only vertebrate animal, not a bird that is able to maintain flight for any duration?
Answer: Bat